Forests and Carbon Sequestration
An overview by Sue Lynn of Cascade Action Now
As climate change has emerged as the major environmental issue of our time, the timber industry is trying to make the case that their current logging practices actually help combat global warming. The big timber companies in California have shifted over the last decade from practices of selective logging to clear-cutting followed by planting tree farms. The timber industry claims that that US could slow down atmospheric accumulation of carbon dioxide if old-growth forests were converted to faster growing, younger, intensively managed forests.1This argument is based on the supposition that the process of planting young tree farms stores more carbon dioxide than it releases. The industry also argues that logging produces wood products that store carbon in long-term storage in buildings and other construction materials, thus decreasing carbon released to the atmosphere.
In each case, the timber industry has seized upon small grains of truth about carbon storage, while badly distorting the overall significance of these facts. Listening to their story is like looking at one frame of a movie to try to understand the entire film.
Let's look at facts, and examine other frames to understand the whole picture.
First, it is true that young trees absorb carbon from the atmosphere and store it more quickly than older trees. But, according to leading forest scientists, the critical factor is the amount of carbon stored within a forest, not the annual rate of carbon uptake.2 One has to look at the entire ecosystem of an older forest, rather than comparing the rate of carbon uptake of a young tree to an older tree. Older forests store much more carbon than younger ones, holding the carbon in their branches, trunks, roots, and leaves, as well as in the soil. Younger forests hold less than half the carbon of older ones. After logging the process of decomposition of carbon stores in the older forest continue for many years. Forest soils are a major carbon sink, usually containing three to four times as much carbon as the vegetation on the ground.3 Using a computer model, researchers found it takes about 200 years for a replanted forest to store as much carbon as an old-growth forest. 4
What happens when a forest is clear-cut and replaced with a tree plantation? After clearcutting, the soil is prepared for replanting by the use of heavy machinery that rips open the soil, allowing organic matter in the soil to rot. That rotting process releases a huge surge of carbon into the atmosphere, more carbon than plantation trees will absorb during their first ten years of growth. Furthermore, leaves and needles release carbon very quickly, while branches and roots and other slash created by logging continue to release more carbon over time. Dr. James Hansen, a top climate scientist who works for NASA has warned that a global tipping point at which global warming becomes unstoppable will be reached in less than ten years. Given the urgency of combating global warming, we must take steps immediately to slow carbon release to the atmosphere, not gamble with the future. The implication of this research is that we must preserve our older forests in order to combat global warming.
Let's look at another frame of this movie. The timber industry claims that the carbon in harvested timber remains in the wood products they sell. Once again, there is partly true; lumber products do store carbon. But what portion of the trees that are cut down actually turn into lumber? A study of Pacific Northwest forests found that approximately 42% of the timber harvested is stored in wood products in buildings and other long-term uses. The rest, however, consists of wood fiber that is left behind, burned, turned into paper, wood chips or mulch, or needles and leaves which fall to the ground, all of which release carbon to the atmosphere.5 And even durable wood products do not necessarily last as long as old-growth trees, which can live hundreds of years.
Tree plantations contribute to global warming in another way: they are highly vulnerable to forest fires, and fires release more carbon into the atmosphere. According to the California Board of Forestry (2005) younger forests are more susceptible to fires due to the lower height and size of small trees. Without large trees with thick bark that can resist fire and provide a cooling canopy for the forest, forest fire danger increases.
Furthermore, clearcutting and global warming interact to exacerbate the effects of one another. Erosion caused by clearcutting results in increased run-off of rain earlier in the spring. At the same time, as the temperature has risen over the last several decades due to global warming, the snowpack has decreased in many recent years and has melted earlier in the spring than usual; in 2007, snowpack in the Sierra Nevada was less than a third of average. The 12-month period from May 2006 to May 2007 was the driest on record for California and Nevada, according to NOAA's National Climactic Data Center.6 Rising temperatures throughout the west will cause more prolonged droughts and wildfires, according to a report from the National Wildlife Federation. 7 As a result, the mountains of California are becoming less effective in playing their historic role of storing water from snow and rain until summer when the water is needed in the valleys. These changes result in forests that dry out earlier in the year, resulting in a significant increase in the number, intensity, and length of forest fires. Those fires then release more carbon into the atmosphere, increasing global warming, which in turn creates more fire danger. This feedback loop is difficult to stop.
As a society we need to tackle global warming through many strategies. One important strategy is managing forests to store as much carbon as possible, which means ending the practice of clearcutting and returning to selective logging, which was the typical harvesting method for timber until the mid-1990s. We must ask the large private timber companies to change their practices before it is too late, and the state of California must make the practice of clearcutting large acreages illegal. If we do not take these steps, global warming will continue to accelerate and threaten the world as we know it.
1. Mark E. Harmon, William K. Ferrell, Jerry F. Franklin, Effects on Carbon Storage of Old-Growth Forests to Young Forests, Science, Feb. 9, 1990.
2. Harmon, Ferrell, Franklin.
3. Tree Farms Won't Halt Climate Change, New Scientist, October 2002.
4. Harmon, Ferrell, Franklin.
6. NOAA National Climactic Data Center reported on www.climatetruth.org.
7. Western Warming Warning, Robert Lee Hotz, Times Staff Writer, 10/06/2006.